In the Shadow of the Transiting Disk: Imaging epsilon Aurigae in Eclipse

Eclipses of the single-line spectroscopic binary star, epsilon Aurigae, provide an opportunity to study the poorly-defined companion. We used the MIRC beam combiner on the CHARA array to create interferometric images during eclipse ingress. Our results demonstrate that the eclipsing body is a dark disk that is opaque and tilted, and therefore exclude alternative models for the system. These data constrain the geometry and masses of the components, providing evidence that the F-star is not a massive supergiant star.Comment: As submitted to Nature. Published in Nature April 8, 2010

New low-resolution spectrometer spectra for IRAS sources

We present low-resolution spectra of 486 IRAS point sources with Fv(12 μm) in the range 20-40 Jy. This is part of an effort to extract and classify spectra that were not included in the Atlas of Low-Resolution Spectra and represents an extension of the earlier work by Volk & Cohen which covers sources with Fv(12 μm) > 40 Jy. The spectra have been examined by eye and classified into nine groups based on the spectral morphology. This new classification scheme is compared with the mechanical classification of the Atlas, and the differences are noted. Oxygen-rich stars on the asymptotic giant branch make up 33% of the sample. Solid state features dominate the spectra of most sources. We find that the nature of the sources as implied by the present spectral classification is consistent with the classifications based on broad-band colors of the sources.link_to_subscribed_fulltex

The UV/X-ray emission of the symbiotic star AG Draconis during quiescence and the 1994/1995 outbursts

We present the results of an extensive campaign of coordinated X-ray (ROSAT) and UV (IUE) observations of the symbiotic star AG Dra during a long period of quiescence followed recently by a remarkable phase of activity characterized by two optical outbursts. The major optical outburst in June 1994 and the secondary outburst in July 1995 were covered by a number of target of opportunity observations (TOO) with both satellites. Optical photometry is used to establish the state of evolution along the outburst. Our outburst observations are supplemented by a substantial number of X-ray observations of AG Dra during its quiescent phase between 1990-1393. Near-simultaneous IUE observations at the end of 1992 are used to derive the spectral energy distribution from the optical to the X-ray range. The X-ray flux remained constant over this three year quiescent phase. The hot component (i.e. X-ray emitting compact object) turns out to be very luminous: a blackbody fit to the X-ray data in quiescence with an absorbing column equal to the total galactic NH in this direction gives (9.5 +/- 1.5) x 10(36) (D/2.5 kpc)(2) erg/s. This suggests that the compact object is burning hydrogen-rich matter on its surface even in the quiescent (as defined optically) state at a rate of (3.2 +/- 0.5) x 10(-8) (D/2.5 kpc)(2) M./yr. Assuming a steady state, i.e. burning at precisely the accretion supply rate. this high rate suggests a Roche lobe filling cool companion though Bondi-Hoyle accretion from the companion wind cannot be excluded. With ROSAT observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux, In the UV these events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AC Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is very likely due to a temperature decrease of the hot component. Such a temperature decrease could be the result of an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size during each optical outburst

Ideas for Citizen Science in Astronomy

We review the relatively new, internet-enabled, and rapidly-evolving field of citizen science, focusing on research projects in stellar, extragalactic and solar system astronomy that have benefited from the participation of members of the public, often in large numbers. We find these volunteers making contributions to astronomy in a variety of ways: making and analyzing new observations, visually classifying features in images and light curves, exploring models constrained by astronomical datasets, and initiating new scientific enquiries. The most productive citizen astronomy projects involve close collaboration between the professionals and amateurs involved, and occupy scientific niches not easily filled by great observatories or machine learning methods: citizen astronomers are most strongly motivated by being of service to science. In the coming years we expect participation and productivity in citizen astronomy to increase, as survey datasets get larger and citizen science platforms become more efficient. Opportunities include engaging the public in ever more advanced analyses, and facilitating citizen-led enquiry by designing professional user interfaces and analysis tools with citizens in mind